1. Field of the Invention
The present invention relates to a semiconductor device, wherein a semiconductor chip is flip-chip-bonded onto a mounting board, and more particularly to an improved thermally stable flip-chip-bonding structure between a semiconductor chip and a mounting board.
2. Description of the Related Art
FIG. 1 is a fragmentary cross sectional view of a conventional flip-chip-bonding structure between a semiconductor chip and a mounting board. A junction layer 23 is adhered through an adhesive layer 25 to a semiconductor chip 21. Electrode pads (not illustrated) are provided on the semiconductor chip 21. A through hole is provided which penetrates the adhesive layer 25 and the junction layer 23. A plug 22 is provided in the through hole, so that the plug 22 is in contact with t e electrode pad.
A metal wiring layer 24 is provided which extends on the junction layer 23, wherein the metal wiring layer 24 is connected through the plug 22 to the through hole. A cover layer 27 is provided which covers the metal wiring layer 24 and the junction layer 23. The cover layer 27 has an opening, through which a solder ball 26 is connected to the metal wiring layer 24. The solder ball 26 is bonded to a non-illustrated wiring which extends over a mounting board 29.
The semiconductor chip 21, the junction layer 23 and the mounting board 29 are made of different materials, and are different from each other in thermal expansion coefficient. Operations of the semiconductor chip 21 generates a heat which is transmitted to the junction layer 23 and the mounting board 29, whereby the semiconductor chip 21, the junction layer 23 and the mounting board 29 show respective different thermal expansions due to the different thermal expansion coefficients. Those different thermal expansions apply a shearing stress to the solder ball 26, whereby a crack 28 appears the solder ball 26. FIG. 2 is a fragmentary cross sectional view of a broken flip-chip-bonding structure of FIG. 1 upon application of shearing stress due to different thermal expansion coefficients,
If the junction layer 23 and the mounting board 29 are made of the same material, then the junction layer 23 receives an influence of thermal expansion of the semiconductor chip 21. For this reason, the junction layer 23 and the mounting board 29 are different in effective thermal extension coefficient, thereby to apply a shearing stress to the solder ball 26, so that the crack 28 also appears the solder ball 26.
In the above circumstances, the development of a novel flip-chip-bonding structure between a semiconductor chip and a mounting board free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel flip-chip-bonding structure between a semiconductor chip and a mounting board free from the above problems.
It is a further object of the present invention to provide a novel thermally stable flip-chip-bonding structure between a semiconductor chip and a mounting board.
It is a further object of the present invention to provide a novel thermally stable flip-chip-bonding structure which is capable of absorbing a stress due to differences in thermal expansion coefficient between the semiconductor chip and the mounting board.
It is a further object of the present invention to provide a novel thermally stable flip-chip-bonding structure which is capable of absorbing a stress due to differences in thermal absorbing coefficient between the semiconductor chip and the mounting board.
It is a further object of the present invention to provide a novel highly reliable flip-chip-bonding structure between a semiconductor chip and a mounting board.
It is a further object of the present invention to provide a novel flip-chip-bonding structure which allows an easy sealing to electrode pads over the semiconductor chip.
It is another object of the present invention to provide a novel method of forming a flip-chip-bonding structure between a semiconductor chip and a mounting board free from the above problems,
It is a further object of the present invention to provide a novel method of forming a thermally stable flip-chip-bonding structure between a semiconductor chip and a mounting board.
It is a further object of the present invention to provide a novel method of forming a thermally stable flip-chip-bonding structure which is capable of absorbing a stress due to differences in thermal expansion coefficient between the semiconductor chip and the mounting board.
It is a further object of the present invention to provide a novel method of forming a thermally stable flip-chip-bonding structure which is capable of absorbing a stress due to differences in thermal absorbing coefficient between the semiconductor chip and the mounting board.
It is a further object of the present invention to provide a novel method of forming a highly reliable flip-chip-bonding structure between a semiconductor chip and a mounting board.
It is a further object of the present invention to provide a novel method of forming a flip-chip-bonding structure which allows an easy sealing to electrode pads over the semiconductor chip.
The present invention provides a semiconductor device comprising: a semiconductor chip having at least an electrode pad; at least a solder material; and at least a bonding-structure for electrically and mechanically bonding the solder material to the electrode pad, wherein the bonding-structure has a flexibility and allows a relative displacement of the solder material in relation to the semiconductor chip.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.